Timothy, Tom,
Thanks for your answers. They are very helpful.
Jim
Thomas Russ <tar at ISI.EDU>
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10/06/2008 02:28 PM
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Re: [protege-owl] Closed world/Open world
On Oct 5, 2008, at 6:11 PM, James A Miller wrote:
>> Hello everyone,
>> This is a follow-up to a statement (from Thomas Russ) in an earlier
> post:
>> "Well, that seems to rely on closed-world reasoning, which is also not
> supported in OWL."
>> I have seen this statement for several years now, but I am curious--
> what is it about OWL in particular that would prevent a reasoner
> from treating the given ontology and data in a closed-world
> fashion? I don't understand how OWL itself enforces open world
> reasoning; it seems that a reasoner could implement a mode that
> treats the data as complete (closed). Why is this not possible?
It is certainly possible to write reasoners like that.
Other description logics(*) have had reasoners that support closed
world assumptions. But that does take you into a different semantic
arena (as Timothy Redmond indicates). One aspect is that closed world
is generally treated as an ASSUMPTION rather than a hard fact, so you
have to introduce a notion of defeasability into the language. It
also requires that you have semantics for non-monotonic reasoning,
since adding new information can cause previous conclusions to have to
be revised.
For example, if you had the following classes:
2-door-car <=> car and exactly 2 has-door
4-door-car <=> car and exactly 4 has-door
and then asserted
car-1 has-door door-1
car-2 has-door door-2
you could satisfy 2-door-car. Adding additional assertions
car-1 has-door door-3
car-1 has-door door-4
would require retracting the previous type classification (2-door-car)
and adding 4-door-car in its place. (Assuming, of course that all of
the doors are different from each other).
-Tom Russ
(*) Loom http://www.isi.edu/isd/LOOM is one such system that I have
been involved in the development of. It has closed-world and other
practical reasoning strategies, but lacks the clearly articulated
semantics of OWL.
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